The present invention relates generally to transmission line systems in electronic devices. More particularly, the invention relates to a technique for transmission line impedance tuning using periodic capacitive stubs.
Electronic devices commonly include a transmission line to route signals to a set of integrated circuits. In such a context, the transmission line may be implemented as a wire on a printed circuit board. A set of such transmission lines forms a bus.
One important design factor for a transmission line is to achieve impedance control within a tight tolerance. Tight impedance control minimizes discontinuities, which in turn minimizes reflection noise, thereby preserving signal quality. Sophisticated techniques are used to design controlled impedance transmission lines in electronic systems. However, once the transmission line is constructed, there are limited techniques available to improve the transmission line""s characteristics.
In view of the foregoing, it would be highly desirable to provide a technique for tuning the performance of a transmission line within a fabricated electronic system.
A method of tuning transmission line impedance includes the step of determining a desired impedance for a transmission line. A set of capacitive stubs is added to the transmission line. A physical quantity to be removed from each of the capacitive stubs to achieve the desired impedance is identified. The identified physical quantity is then removed to establish the desired transmission line impedance.
A method of forming an impedance bridge includes the step of affixing a set of capacitive stubs to a bridging transmission line that has a first end and a second end. The vertical height of the set of capacitive stubs is tapered from the first end to the second end to form an increasingly high impedance between the first end and the second end.